Cover tape for packaging electronic components

ABSTRACT

For solving a problem of large dependency of peel-off strength upon sealing conditions, a problem of change of various properties with the lapse of time under storing circumstances, a delamination problem, an agglomerate problem and a transparency problem, there is provided a cover tape for packaging electronic components which has a stable peel-off strength and is composed of an outer layer consisting of a biaxially oriented film of any one of polyester, polypropylene and nylon; an intermediate layer consisting of a mixture comprising polyethylene as the main component; and a heat sealant layer consisting of a mixture of a thermoplastic resin and a filler.

TECHNICAL FIELD

This invention relates to a cover tape heat-sealable sealable to aplastic carrier tape having storing pockets formed therein, whichcarrier tape is one of the packages having such a function that whenelectronic components are stored, transported or mounted, the electroniccomponents are protected from contamination, and arranged and taken outfor mounting them on an electronic circuit substrate.

BACKGROUND ART

Recently, surface mount electronic components such as IC, transistor,diode, condenser, piezoelectric element resistor and the like have beenpacked into a package composed of a plastic carrier tape havingsuccessively formed therein emboss-molded pockets into which theelectronic components can be received in conformity with the shapes ofthem, and a cover tape heat-sealable to the carrier tape, and thensupplied. The electronic components packed are automatically taken outfrom the package after the cover tape has been peeled from the carriertape, and then surface mounted on an electronic circuit substrate.

The strength for peeling the cover tape from the carrier tape is called"peel-off strength", and when this strength is too low, there is such aproblem that the cover tape gets off during the transportation of thepackage and the electronic components packed fall off. On the otherhand, when the strength is too high, there has been caused such aphenomenon that the carrier tape vibrates when the cover tape is peeledand the electronic components jump out of the storing pockets justbefore they are mounted, that is, a jumping trouble has been caused.

The mechanism by which the cover tape now on the market peels from thecarrier tape is classified into three types of interfacial peeling type,transfer-peeling type and cohesive failure type. The interfacial peelingtype refers to such a type that the cover tape and the carrier tape arepeeled from each other at the sealing face, the transfer peeling typerefers to such a type that the bonding layer per se is transferred tothe carrier tape during the peeling, and the cohesive failure typerefers to such a type that a layer different from the bonding layer orthe bonding layer per se (the two being referred to hereinafter as thecohesive failure layer) is broken to cause peeling. Each of these typeshas both merits and demerits; however, when they are compared only inrespect of the state in which the cover tape sealed to the carrier tapeis peeled, the interfacial peeling type tends to be affected by theshape, material and properties of the carrier tape because the sealingface and the peeling face are the same, and hence the peel-off strengthtends to become instable.

In the case of the transfer-peeling type, the bonding layer must be athin film in view of the mechanism and the so-called heat-sealinglacquer must be used. Therefore, the peel-off strength tends to becomesensitive to sealing temperature, and hence sealing conditions for asuitable peel-off strength are hardly obtained.

In the case of the cohesive failure type, the sealing face and thepeeling layer are different, and hence the dependency of the peel-offstrength upon the sealing conditions is low. Also, the cohesive failuretype has such a great advantage that the peel-off strength is notaffected by the shape, material and properties of the carrier tape.However, in some cases, during the peeling, the cohesive failure layeris affected by a layer other than the cohesive failure layer includingthe bonding layer and interfacial peeling takes place without causingcohesive failure. Also, it is difficult to decide the position at whichthe cohesive failure layer is broken, and hence the cohesive failurelayer remains on the surface of the carrier tape during the peeling andthere is brought about such a state that the contents cannot be takenout.

The cohesive failure layer per se is designed so as to be easily broken,and hence in many cases, it is composed of a mixture of a plurality ofresins which are hardly miscible with one another and these resins arenot mixed uniformly. This results in a deterioration of the transparencyof the cover tape and in a disadvantage due to agglomerates in somecases. Also, in such uses, a resin inferior in heat resistance iscontained in the resin mixture in some cases. For these reasons, theagglomerates or degradation products appear during the formation of thecohesive failure layer and decrease the productivity in many cases. Forexample, Japanese Patent No. 1,347,759 (Applicant: UCB Societe Anonyme)recites in claim 5 a blend of polyethylene, polystyrene and anelastomeric styrene-butadiene-styrene or styrene-isoprene-styrene blockcopolymer, and when the blend is used to try the formation of thecohesive failure layer, the butadiene or isoprene component causespolymerization reaction when the processing temperature exceeds 200° C.to produce an agglomerate, resulting in a remarkable decrease of theproduction yield.

DISCLOSURE OF THE INVENTION

The object of this invention is to obtain such a cover tape that thepeel-off strength does not depend upon sealing temperature when thecover tape is peeled from a carrier tape, the change of variousproperties with the lapse of time under the storage circumstances issmall and the sealability is stable, by utilizing the mechanism ofpeeling due to cohesive failure.

According to this invention, there is provided a cover tape forpackaging electronic components which cover tape is heat sealable to aplastic carrier tape, characterized in that the cover tape is composedof a biaxially oriented film of any one of polyester, polypropylene andnylon; a heat sealant layer consisting of a mixture of 100 parts byweight of a thermoplastic resin having a softening point of 40° C. to130° C. and 1 to 60 parts by weight of a filler having a particle sizeof 0.2 to 20 μm; and an intermediate layer comprising polyethylene asthe main component provided between the biaxially oriented film and theheat sealant layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the layer constitution of thecover tape of this invention.

FIG. 2 is a cross-sectional view showing the state in which the covertape of this invention is bonded to a carrier tape.

In FIGS. 1 and 2, 1 refers to a cover tape, 2 to a biaxially orientedfilm, 3 to an intermediate layer, 4 to a heat sealant layer, 5 to aportion to be heat-sealed and 6 to a carrier tape.

BEST MODE FOR CARRYING OUT THE INVENTION

In preferable embodiments of the cover tape for packaging electroniccomponents of this invention, the biaxially oriented film as the outerlayer has a thickness of 5 to 30 μm; the intermediate layer has athickness of 5 to 50 μm and is composed of a mixture of 100 parts byweight of a polyethylene having a melt flow rate of 10 to 30 g/10 minand 5 to 100 parts by weight of a polystyrene having a melt flow rate of10 to 30 g/10 min, or a mixture obtained by adding to the above mixture1 to 50 parts by weight of at least one member selected from the groupconsisting of a hydrogenated styrene-butadiene-styrene block copolymerhaving a melt flow rate of 30 to 250 g/10 min and a hydrogenatedstyrene-isoprene-styrene block copolymer having a melt flow rate of 30to 250 g/10 min; the heat sealant layer has a thickness of 0.2 to 3 gmand is composed of a mixture of 100 parts by weight of apolymethacrylate having a softening temperature of 40 to 130° C. or avinyl chloride-vinyl acetate copolymer having a softening temperature of40 to 130° C. and 1 to 60 parts by weight of a filler having a particlesize of 0.2 to 20 μm which is composed of at least one member selectedfrom the group consisting of silica, talc, calcium carbonate, clay,polyethylene particles, cross-linked acrylic resin particles andcross-linked styrene resin particles; and the pealing strength betweenthe cover tape and the carrier tape is 10 to 120 g/mm of seal width.

Referring to FIG. 1, the constituents of the cover tape 1 of thisinvention are explained. The outer layer 2 is a biaxially oriented filmof any one of polyester, polypropylene and nylon and is a transparent,highly rigid film having a thickness of 5 to 30 μm. When the thicknessis less than 5 μm, the rigidity is lost and the cover tape tends to bebroken. When the thickness exceeds 30 μm, the film is too hard and theseal becomes instable.

In order to enable the cohesive failure to take place, the intermediatelayer 3 is a film having a thickness of 5 to 50 μm composed of a mixtureof 100 parts by weight of a polyethylene having a melt flow rate of 10to 30 g/10 min and 5 to 100 parts by weight of a polystyrene having amelt flow rate of 10 to 30 g/10 min, or a mixture of 100 parts by weightof a polyethylene having a melt flow rate of 10 to 30 g/10 min, 5 to 100parts by weight of a polystyrene having a melt flow rate of 10 to 30g/10 min and 1 to 50 parts by weight of at least one member selectedfrom the group consisting of a hydrogenated styrene-butadiene-styreneblock copolymer having a melt flow rate of 30 to 250 g/10 min and ahydrogenated styrene-isoprene-styrene block copolymer having a melt flowrate of 30 to 250 g/10 min. The intermediate layer is preferablyprepared by an extrusion-laminating method because this method isinexpensive and desirable from a hygienic point of view.

When the melt flow rate of the polyethylene is less than 10 g/10 min orthe melt flow rate of the polystyrene is less than 10 g/10 min, or whenthe melt flow rate of the hydrogenated styrene-butadiene-styrene blockcopolymer or the hydrogenated styrene-isoprene-styrene block copolymeris less than 30 g/10 min, the malleability of a film formed by theextrusion-laminating method is small and a suitable film formation isimpossible. Moreover, when the melt flow rate of the polyethylene ismore than 30 g/10 min or the melt flow rate of the polystyrene is morethan 30 g/10 min, or when the melt flow rate of the hydrogenatedstyrene-butadiene-styrene block copolymer or hydrogenatedstyrene-isoprene-styrene block copolymer is more than 250 g/10 min, thenecking is violent and hence a suitable film formation is impossible.

The polystyrene content is less than 5 parts by weight per 100 parts byweight of the polyethylene, no cohesive failure takes place in theintermediate layer. When it is more than 100 parts by weight, themiscibility becomes low and the film formation becomes impossible. Whenthe content of the hydrogenated styrene-butadiene-styrene blockcopolymer and/or the hydrogenated styrene-isoprene-styrene blockcopolymer is less than 1 part by weight per 100 parts by weight of thepolyethylene, the visible light transmittance of the film becomes 75% orless. When the content is more than 50 parts by weight, a variation infilm thickness is caused in the extrusion-lamination. When the thicknessof the intermediate layer is adjusted to less than 5 μm by theextrusion-laminating method the variation in thickness becomes large anda suitable peel-off strength is not obtained. When the thickness is morethan 50 μm, such a phenomenon that the cohesive layer remains on thesurface of the carrier tape during the peeling tends to take place.

The outer layer and the intermediate layer may be laminated through abonding layer of a thermosetting type such as an isocyanate type, animine type or the like or a thermoplastic type such as polyethylene orthe like for the purpose of increasing the laminate strength of the twolayers.

Preferably the heat sealant layer 4 has a thickness of 0.2 to 3 μm andis composed of a mixture of 100 parts by weight of a polymethacrylate ora vinyl chloride-vinyl acetate copolymer and 1 to 60 parts by weight ofa filler having a particle size of 0.2 to 20 μm composed of at least onemember selected form the group consisting of silica, talc, calciumcarbonate, clay, polyethylene particles, cross-linked acrylic resinparticles and cross-linked styrene resin particles. Since this layer isa very thin film, it is most preferably prepared by a gravure coatingmethod. As the polymethacrylate, there is mentioned, for example, methylmethacrylate-butyl methacrylate copolymer. The softening temperature ofthe copolymer can be varied in the range of from 40° C. to 130° C. bychanging the copolymerization ratio. As the vinyl chloride-vinyl acetatecopolymer, there are mentioned, for example, Dicseal A-100Z series(manufactured by DAINIPPON INK & CHEMICALS, INC.). The softeningtemperatures thereof vary depending upon the product number. When thesoftening temperature is less than 40° C., there is a possibility thatblocking is caused when the cover tape is stored, and when the softeningtemperature exceeds 130° C., it is necessary to elevate the temperaturefor heat sealing and in this case there is a fear that the carrier tapeper se may be broken.

When the particle size of the filler is less than 0.2 μm or the contentof the filler is less than 1 part by weight, there is caused theso-called blocking phenomenon that when the cover tape is stored underhigh temperature circumstances of not less than 60° C. the rewindingbecomes impossible. Moreover, when the particle size of the filler ismore than 20 μm or the content of the filler is more than 60 parts byweight, the transparency becomes bad and the visible light transmittancebecomes less than 75%. When the thickness of the heat sealant layer isless than 0.2 μm, it is very difficult to make the thickness constantand it becomes impossible to obtain a stable peel-off strength. When thethickness is more than 3 μm, cohesive failure takes place in the heatsealant layer and the peel-off strength becomes instable as well.

In order to improve the antistatic effect, both sides of the outerlayer, namely the biaxially oriented film may be provided with anantistatic treatment layer or an electroconductive layer.

The resin of the intermediate layer is so constituted that the bondingstrength between the cover tape 1 and the carrier tape 6 becomes 10 to120 g/mm of seal width, preferably 10 to 70 g/mm of seal width. When thepeel-off strength is lower than 10 g, there is such a problem that thecover tape gets off during the transportation of the package and theelectronic components contained fall out. On the contrary, when thepeel-off strength is more than 120 g, the carrier tape is vibrated whenthe cover tape is peeled, and such a phenomenon that the electroniccomponents are jumped out of the storing pockets just before themounting thereof, namely a jumping trouble, is caused. According to thisinvention, there can be obtained the desired properties that thedependency upon the sealing conditions is low and the change of thepeel-off strength with the lapse of time under storage circumstances issmall.

Moreover, the cover tape is so constituted that the visible lighttransmittance becomes not less than 75%, preferably not less than 80%,and hence the electronic components sealed into the carrier tape can beconfirmed visually or mechanically. When the above transmittance is lessthan 75%, it is difficult to confirm the electronic components in thecarrier tape.

Examples are shown below to explain this invention in more detail;however, they are merely illustrative and not limitative.

EXAMPLES 1 TO 7 AND COMPARATIVE EXAMPLES 1 TO 6

Using the formulation shown in Table 1 or Table 2, on a biaxiallyoriented polyester film having a thickness of 25 μm, an intermediatelayer having a thickness of 30 μm was formed by an extrusion-laminatingmethod (extrusion temperature: 280° C.) and a heat sealant layer havinga thickness of 1 μm was formed by a gravure coating method to obtain acover tape having the layer constitution shown in FIG. 1. The cover tapeobtained was slit in a width of 5.3 mm and thereafter this slit covertape and a PET carrier tape having a width of 8 mm were subjected toheat sealing. The resulting assembly was subjected to measurement ofpeeling mechanism, peel-off strength, visible light transmittance andthe state of blocking when the cover tape was stored at an ambienttemperature of 60° C. The results of evaluation of the characteristicsobtained are shown in Table 1 with respect to the Examples and in Table2 with respect to the Comparative Examples.

                  TABLE 1                                                         ______________________________________                                                 Example                                                                              Example   Example  Example                                             1      2         3        4                                          ______________________________________                                        Inter-                                                                              Poly-    100      100     100    100                                    mediate                                                                             ethylene                                                                layer Poly-    30       30      30     30                                     formu-                                                                              styrene                                                                 lation                                                                              SEBS     45       45       7      0                                           SEPS      0        0       0     30                                     Heat  Thermo-  Acryl    VC-VA   Acryl  Acryl                                  sealant                                                                             plastic  100      100     100    100                                    layer resin                                                                   formu-                                                                              Filler   Cross-   Silica  Cross- Cross-                                 lation         linked           linked linked                                                acryl            styrene                                                                              acryl                                                 55       30       2     55                                           (particle                                                                               (7)      (3)    (12)   (7)                                          size) (μm)                                                           Visible light                                                                            77       76        87     78                                       transmittance                                                                 Peel-off strength                                                                        45       30        54     43                                       Initial value                                                                 (g/mm of seal                                                                 width)                                                                        State of blocking                                                                        ◯                                                                          ◯                                                                           ◯                                                                        ◯                            Peeling mechanism                                                                        Cohesive Cohesive  Cohesive                                                                             Cohesive                                            failure  failure   failure                                                                              failure                                  ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________             Compara-                                                                           Compara-                                                                           Compara-                                                                           Compara-                                                                           Compara-                                                                           Compara-                                             tive tive tive tive tive tive                                                 Example 1                                                                          Example 2                                                                          Example 3                                                                          Example 4                                                                          Example 5                                                                          Example 6                                   __________________________________________________________________________    Inter-                                                                            Poly-                                                                              100  100  100  100  100  100                                         mediate                                                                           ethylene                                                                  layer                                                                             Poly-                                                                                 4 110  30   30    4   110                                         formu-                                                                            styrene                                                                   lation                                                                            SEBS  0    0   70    7    7    7                                          Heat                                                                              Thermo-                                                                            VC-VA                                                                              Acryl                                                                              VC-VA                                                                              Acryl                                                                              VC-VA                                                                              Acryl                                       sealant                                                                           plastic                                                                            100  100  100  100  100  100                                         layer                                                                             resin                                                                     formu-                                                                            Filler                                                                             Talc Silica                                                                             Wax  Cross-                                                                             Silica                                                                             Cross-                                      lation                  linked    linked                                                              acryl     styrene                                              70   0.5  40   0.5  30    2                                              (particle                                                                          (3)  (1.4)                                                                              (10) (30) (0.1)                                                                              (12)                                            size) (μm)                                                             Visible light                                                                          64   70   71   64   84   72                                          transmittance                                                                 Peel-off strength                                                                        10 72   12   55    8   67                                          Initial value (g/mm                                                           of seal width)                                                                State of blocking                                                                      ◯                                                                      x    ◯                                                                      x    x    ◯                               Peeling mechanism                                                                      Inter-                                                                             Cohesive                                                                           Inter-                                                                             Cohesive                                                                           Inter-                                                                             Cohesive                                             facial                                                                             failure                                                                            facial                                                                             failure                                                                            facial                                                                             failure                                              peeling   peeling   peeling                                          __________________________________________________________________________     Notes to Tables 1 and 2                                                       Heat sealing conditions: 160° C./1 kg/cm.sup.2 /0.1 sec, seal widt     0.4 min × 2                                                             Peeling conditions: 180° peeling, peeling speed 300 mm/min, n = 3      The numerals in the intermediate formulation are parts by weight per 100      parts by weight of polyethylene.                                              The numerals in the heat sealant layer formulation are parts by weight of     filler per 100 parts by weight of the thermoplastic resin.                    State of blocking:                                                            ◯: No blocking,                                                   x: blocking was caused and the tape was not practical.                        VCVA: Vinyl chloridevinyl acetate copolymer having a softening temperatur     of 45° C. (Dickseal A100Z-5A manufactured by DAINIPPON INK &           CHEMICALS, INC.)                                                              Acryl: Methyl methacrylatebutyl methacrylate copolymer having a softening     temperature of 60° C. (manufactured by Osaka Printing Ink MFG Co.,     Ltd.)                                                                         Talc: Inorganic filler comprising magnesium silicate hydrate mineral as       the main component (Microace L1 manufactured by Nippon Talc Co., Ltd.)        Wax: polyethylene wax.                                                        Crosslinked acryl: Crosslinked acrylic resin (manufactured by Soken Kagak     K. K.)                                                                        Crosslinked styrene: Crosslinked styrene resin (manufactured by Soken         Kagaku K. K.)                                                                 Silica: Inorganic filler comprising silicon dioxide as the main component     Melt flow rate of polyethylene: 20 g/10 min                                   Melt flow rate of polystyrene: 22 g/10 min                                    SEBS: Hydrogenated styrenebutadiene-styrene block copolymer having a melt     flow rate of 120 g/10 min                                                     SEPS: Hydrogenated styreneisoprene-styrene block copolymer having a melt      flow rate of 150 g/10 min                                                

Industrial Applicability

This invention provides a cover tape which is not affected by variationin sealing conditions during sealing, is free from change of variousproperties with the laps of time and has a stable peeling strength. Thiscover tape is a very advantageous cover tape for packaging electroniccomponents which can be used as a cover material for a carrier tapesystem for storing and transporting electronic components.

I claim:
 1. A cover tape for packaging electronic components which covertape is heat sealable to a plastic carrier tape, characterized in thatthe cover tape is composed of a biaxially oriented film of any one ofpolyester, polypropylene and nylon; a heat sealant layer consisting of amixture of 100 parts by weight of thermoplastic resin having a softeningtemperature of 40° C. to 130° C. and 1 to 60 parts by weight of a fillerhaving a particle size of 0.2 to 20 μm; and an intermediate layerbetween the biaxially oriented film and the heat sealant layer, and saidintermediate layer is composed of a resin composition consisting of 100parts by weight of a polyethylene having a melt flow rate of 10 to 30g/10 min, 5 to 100 parts by weight of a polystyrene having a melt flowrate of 10 to 30 g/10 min and 1 to 50 parts by weight of at least onemember selected from the group consisting of a hydrogenatedstyrene-butadiene-styrene block copolymer having a melt flow rate of 30to 250 g/min and a hydrogenated styrene-isoprene-styrene block copolymerhaving a melt flow rate of 30 to 250 g/10 min; said biaxially orientedfilm has a thickness of 5 to 30 μm, the intermediate layer has athickness of 5 to 50 μm, and the heat sealant layer has a thickness of0.2 to 3 μm, and wherein said resin of the intermediate layer is soconstituted that the peel strength between the cover tape and thecarrier tape becomes 10 to 120 g/mm of seal width.
 2. The cover tape forpackaging electronic components according to claim 1, characterized inthat the thermoplastic resin in the heat sealant layer is apolymethacrylate or a vinyl chloride-vinyl acetate copolymer.
 3. Thecover tape for packaging electronic components according to claim 1,wherein the filler is composed of at least one member selected from thegroup consisting of silica, talc, calcium carbonate, clay, polyethyleneparticles, cross-linked acrylic resin particles and cross-linked styreneresin particles.